Method for controlling the speed of a vehicle

ABSTRACT

In a method for controlling a speed of a vehicle, when an actual speed of the vehicle exceeds a predefined setpoint speed by more than a first predefined speed difference, a service brake of the vehicle is activated. In the method, the first predefined speed difference has a value greater than zero. Also, when the actual speed exceeds the setpoint speed by a second predefined speed difference, which is smaller than the first predefined speed difference, an idle speed control can be activated and a torque request of activated ancillary components can be reduced. Further, when the actual speed exceeds the setpoint speed by a sixth predefined speed difference, which is smaller than the first predefined speed difference, an ancillary component can be activated.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a division of U.S. patent application Ser.No. 10/519,369 filed on Sep. 8, 2005, which in turn was a national-phaseapplication based on international application PCT/DE03/00292 filed onFeb. 3, 2003, and claimed priority to German Application DE 10231360.1filed on Jul. 11, 2002.

BACKGROUND INFORMATION

From German Patent Application No. DE 195 37 273 it is known to triggerwear-free, additional deceleration devices such as retarders with theaid of a speed control. Retarders, and engine brakes as well, may beused to maintain a constant vehicle speed on a downhill grade in thoseinstances where an intervention in the engine control alone may beinsufficient to maintain a slow speed. The additional decelerationdevices must be differentiated from the service brakes of a vehicle.

SUMMARY OF THE INVENTION

The method according to the present invention for controlling the speedof a motor vehicle has the advantage that a service brake of the vehicleis activated when an actual speed of the vehicle exceeds a predefinedsetpoint speed by more than a first predefined speed difference. In thisway the functionality of the driving speed control may be expanded insuch a way that the speed is able to be maintained on downhill roadsections, for instance, even in those cases where the drag torque of thevehicle's drive train fails to generate sufficient braking action. Thedriving speed control may thus be utilized to a greater extent, whichincreases the driving comfort.

It is particularly advantageous if the service brake is activated onlywhen other measures, such as reducing the torque demand of the drivingspeed control, an idle speed control, a deceleration fuel cutoff and/oran additional activation of one or a plurality of ancillary componentsdo not lead to sufficient braking action to adequately adjust the actualspeed of the vehicle to the predefined setpoint speed. In this way thedriving speed control, and thus the service brake, may be realized in agentle manner prior to activation of the service brake, by utilizing theengine braking action. If the service brake is activated in additionwhen the engine braking action is active, stronger braking action may beachieved and the driving speed control maintained even in a pronounceddownhill gradient, i.e., the actual speed of the vehicle may besufficiently adjusted to or brought within the range of the predefinedsetpoint speed in the case of a steep downhill gradient as well.

Another advantage is that the service brake will be deactivated when theactual speed drops below the setpoint speed again. With appropriateselection of the first predefined speed difference, a continualdeactivation and activation of the service brake is avoided, whichincreases the driving comfort.

It is particularly advantageous if the idle speed control is deactivatedfor as long as the service brake is activated. This saves fuel when theservice brake is activated.

Support of the service brake by the engine brake may be obtained byactivating the deceleration-fuel cutoff for as long as the service brakeremains activate.

Another advantage results if the fuel cutoff on deceleration isactivated when the actual speed exceeds the setpoint speed by a fourthpredefined speed difference, which is greater than a second predefinedspeed difference at which the idle-speed control is activated. Thisactivates the fuel cutoff on deceleration only if the braking actionachieved by the idle speed control has been insufficient duringadjustment of the actual speed of the vehicle to the predefined setpointspeed. This increases the driving comfort, since it avoids an excessivelowering of the torque as it happens in a direct fuel cutoff ondeceleration without prior idle speed control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram with components for realizing the methodaccording to the present invention.

FIG. 2 shows a flow chart for an exemplary sequence of the methodaccording to the present invention.

FIG. 3 a shows the profile of the actual speed of the vehicle over time.

FIG. 3 b shows the profile of the torque request of the driving speedcontrol over time.

FIG. 3 c shows the profile of the idle speed control over time.

FIG. 3 d shows the profile of the fuel cutoff on deceleration over time.

FIG. 3 e shows the profile of a request to the service brake of thevehicle over time.

DETAILED DESCRIPTION

Reference numeral 10 in FIG. 1 denotes a control unit of a motorvehicle, which is connected to a service brake 1 of the motorvehicle—generally a friction brake that is subject to wear—, an idlespeed control 5, one or more ancillary components 15, and a drivingspeed control 20. In addition, a speedometer 25 is provided, whichmeasures the actual speed of the vehicle and is connected to vehiclecontrol 10 and driving speed control 20. Speedometer 25 transmits theactual instantaneous speed of the vehicle to vehicle control 10 anddriving speed control 20.

In this exemplary embodiment vehicle control 10 constitutes an expandedengine control, which not only controls the engine of the vehicle butservice brake 1 of the vehicle as well.

In the activated state, driving speed control 20 transmits a torquerequest to vehicle control 10, which vehicle control 10 implements in amanner not shown, by appropriate adjustment of the ignition firingpoint, the injection duration or the air supply into the combustionchamber of the motor vehicle, for instance.

FIG. 2 describes the method according to the present invention on thebasis of a flow chart by way of example. The program is started uponactivation of driving speed control 20, for instance by the driver ofthe vehicle using a cruise control lever. In a program point 100 drivingspeed control 20 checks whether the actual speed of the vehicle isgreater than the predefined setpoint speed. If this is the case, theprogram branches to program point 105, otherwise the program branches toa program point 155.

In program point 155 the current torque request of driving speed control20 will be maintained if the actual speed corresponds to the predefinedsetpoint speed, or it will be raised if the instantaneous speed is lowerthan the predefined setpoint speed. The method subsequently branchesback to program point 100.

In program point 105 driving speed control 20 reduces the torque requestto vehicle control 10. The torque request may be reduced by a suitablyselected predefined decremental value, for instance, and the increase inthe torque request, described in connection with program point 155, maybe realized by a likewise suitably selected, predefined incrementalvalue. After program point 105 the program branches to a program point110.

In program point 110 driving speed control 20 ascertains whether theactual speed exceeds the predefined setpoint speed by more than a secondpredefined speed difference. If this is the case, the program branchesto a program point 115, otherwise the program branches back to programpoint 100.

In program point 115 an activation signal is set in driving speedcontrol 20 and transmitted to vehicle control 10. Upon receipt of theset activation signal, vehicle control 10 initiates an activation ofidle speed control 5 in program point 115, thereby reducing the torquerequest of the activated ancillary components of the vehicle, such asthe air condition system or the generator. The program then branches toa program point 120.

In program point 120 vehicle control 10 checks whether the actual speedexceeds the predefined setpoint speed by less than a third predefinedspeed difference, which is smaller than the second predefined speeddifference. If this is the case, the program branches to a program point150, otherwise the program branches to a program point 125.

In program point 150 vehicle control 10 initiates a deactivation of idlespeed control 5. As soon as driving speed control 20 determines that theactual speed once again exceeds the predefined setpoint speed by lessthan the third predefined speed difference, it initiates the resettingof the activation signal. After program point 150, the program branchesback to program point 100.

In program point 125 vehicle control 10 ascertains whether the actualspeed exceeds the predefined setpoint speed by more than a fourthpredefined speed difference, which is greater than the second predefinedspeed difference. If this is the case, the program branches back to aprogram point 130, otherwise the program branches to program point 120.

In program point 130 vehicle control 10 initiates the activation of afuel cutoff on deceleration of the vehicle by interrupting the injectionof fuel, for instance, and it deactivates idle speed control 5. Theprogram then branches to a program point 140.

In program point 140 vehicle control 10 ascertains whether the actualspeed exceeds the predefined setpoint speed by less than a fifthpredefined speed difference, which is greater than the second predefinedspeed difference and smaller than the fourth predefined speeddifference. If this is the case, the program branches to a program point145, otherwise the program branches to a program point 165.

In program point 145 vehicle control 10 initiates a deactivation of thedeceleration fuel-cutoff, i.e., in this example, it restores the fuelsupply. Vehicle control 10, using an additional suitable activationsignal, for instance, subsequently causes driving speed control 20 toresume the program in program point 110.

In program point 165 vehicle control 10 ascertains whether the actualspeed exceeds the predefined setpoint speed by more than a sixthpredefined speed difference, which is greater than the fourth predefinedspeed difference. If this is the case, the program branches to a programpoint 170, otherwise the program branches back to program point 140.

In program point 170 vehicle control 10 initiates the activation of oneor more previously non-activated ancillary components, which requireadditional drag torque in an the activated deceleration fuel-cutoff andthereby generate additional braking action. If no further activatableancillary components are present in the vehicle and provided the actualspeed exceeds the predefined setpoint speed by more than the sixthpredefined speed difference, it is branched from program point 165directly to a program point 185. However, if program point 170 isexecuted, branching to a program point 175 will take place subsequently.

In program point 175 vehicle control 10 ascertains whether the actualspeed exceeds the predefined setpoint speed by less than a seventhpredefined speed difference, which is smaller than the sixth predefinedspeed difference and greater than the fourth predefined speeddifference. If this is the case, the program branches to a program point180, otherwise the program branches to program point 185.

In program point 180 vehicle control 10 initiates a deactivation andthus deenergization of the ancillary component(s) which had additionallybeen activated or energized in program point 170. The method thenbranches back to program point 125.

In program point 185 vehicle control 10 ascertains whether the actualspeed exceeds the predefined setpoint speed by more than a firstpredefined speed difference, which is greater than the sixth predefinedspeed difference. If this is the case, branching to a program point 190will take place; otherwise, in the event that one or more additionalancillary components had been switched on or activated in program point170, it is branched back to program point 175. However, if the actualspeed does not exceed the predefined setpoint speed by more than thefirst predefined speed difference, it is branched from program point 185back to program point 140.

In program point 190, vehicle control 10 initiates an activation ofservice brake 1 of the vehicle, whereupon the program branches to aprogram point 195.

In program point 195 vehicle control 10 checks whether the actual speedis lower than the predefined setpoint speed. If this is the case, theprogram is exited, otherwise the program branches back to program point195. If the actual speed is less than the predefined setpoint speed,this is also detected by vehicle control 20, which then resets theactivation signal it had set.

If driving speed control 20 is still active the described program willbe run through again.

In FIG. 3 a the method according to the present invention is illustratedwith the aid of an exemplary profile of the difference between theactual speed of the vehicle and the predefined setpoint speed over timet. The actual speed is denoted by v_act, and the predefined setpointspeed is denoted by v_setpoint, so that the difference plotted over theordinate is v_act—v_setpoint. For the difference v_act—v_setpoint, thefirst predefined speed difference is denoted on the ordinate, byKLDVBROB, and amounts to 4 km/h, for example.

The second predefined speed difference is denoted by DVLLVO in FIG. 3 aand amounts to 2 km/h by way of example. The third predefined speeddifference is denoted by DVLLVU in FIG. 3 a and amounts to 1.5 km/h, forinstance. The fourth predefined speed difference is denoted by DVSAVO inFIG. 3 a and amounts to 3 km/h by way of example. The fifth predefinedspeed difference is denoted by DVSAVU in FIG. 3 a and amounts to 2.5km/h, for instance. The sixth and seventh predefined speed differencesare not shown in FIG. 3 a since it is assumed in this example that noadditional ancillary components will be activated.

Second predefined speed difference DVLLVO and third predefined speeddifference DVLLVU bring about a hysteresis and prevent a continualactivation and deactivation of idle speed control 5 when differencev_act−v_setpoint fluctuates by the second predefined speed differenceDVLLVO. Correspondingly, fourth predefined speed difference DVSAVO andfifth predefined speed difference DVSAVU cause a hysteresis and preventa continual switch between deceleration fuel-cutoff and idle speedcontrol when difference v_act−v_setpoint fluctuates by the fourthpredefined speed difference DVSAVO.

In addition, the present invention may provide that service brake 1,activated for controlling the driving speed, is deactivated again onlywhen predefined setpoint speed v_setpoint exceeds actual speed v_act bymore than a predefined termination value, which is denoted by DVLLVUBRin FIG. 3 a. For the flow chart shown in FIG. 2 this means that vehiclecontrol 10 checks at program point 195 whether the predefined setpointspeed exceeds the actual speed by more than the predefined terminationvalue DVLLVUBR. If this is the case, the program is exited, otherwisethe program branches back to program point 195. In this manner ahysteresis is also realized for the activation of the service brake tocontrol the driving speed, such hysteresis preventing an excessiveswitching between the engine brake and the service brake of the vehicle.

In FIG. 3 a, difference v_act−v_setpoint increases from instant t=0 upto a first instant t₁ and reaches second predefined speed differenceDVLLVO at first instant t1. FIG. 3 b shows the torque request of thedriving speed control over time t, the torque request being denoted bymrfgr_w. The increase in difference v_act−v_setpoint up to first instantt₁ results in a reduction of torque request mrfgr_w down to zero evenbefore first instant t₁ is reached. FIG. 3 c, by means of a logicalvalue, illustrates over time t whether or not idle speed control 5 isactivated. In FIG. 3 d it is shown over time t with the aid of a logicalvalue whether or not the deceleration fuel-cutoff is activated. FIG. 3 eillustrates over time t by means of a logical value whether a brakerequest for the activation of service brake 1 is present for drivingspeed control 20.

From instant t=0 to first instant t₁ the logical values for the idlespeed control, deceleration fuel-cutoff and the brake request are equalto zero, i.e., the idle speed control, the deceleration fuel-cutoff andthe service brake are not activated. At instant t₁, differencev_act−v_setpoint exceeds the second predefined speed difference DVLLVO.This leads to the activation of the idle speed control whose logicalvalue is set at instant t₁. The logical values for the decelerationfuel-cutoff and the brake request remain equal to zero, so that thedeceleration fuel-cutoff and the service brake continue to bedeactivated. Since torque request mrfgr_w has gone back to zero evenbefore first instant t₁ was reached, the torque request of the activatedancillary components is able to be reduced as well by activation of theidle speed control, so that an additional braking action is achieved bythe drag torque of the drive unit of the vehicle. Differencev_act−v_setpoint continues to increase from first instant t₁ up to asecond instant t₂, and at second instant t₂ exceeds fourth predefinedspeed difference DVSAVO. At second instant t₂ the logical value for thedeceleration fuel-cutoff is therefore set and the decelerationfuel-cutoff activated, whereas the idle speed control is deactivated atsecond instant t₂ and the logical value for the idle speed control isreset. The logical value for the brake request continues to remain equalto zero, so that service brake 1 stays deactivated. Due to thedeceleration fuel-cutoff, the engine braking initiated by idle speedcontrol 5 is amplified in its effect as a result of the fuel supplybeing switched off. Any torque requests of the activated ancillarycomponents are reduced to zero in the process. Since idle speed control5 is activated between first instant t₁ and second instant t₂, thetransition to the point where the torque requests of the activatedancillary components are reduced to zero will not occur abruptly, sothat the driving comfort is not overly affected.

First instant t₁ follows instant t=0. Second instant t₂ follows firstinstant t₁.

Between second instant t₂ and a subsequent third instant t₃, differencev_act−v_setpoint reaches a maximum value, which is smaller than firstpredefined speed difference KLDVBROB, however, so that service brake 1will not be activated. Due to the braking action achieved by theactivated deceleration fuel-cutoff, difference v_act−v_setpoint thendrops again, and at third instant t₃ falls below fifth predefined speeddifference DVSAVU. At third instant t₃, the deceleration fuel-cutoff istherefore deactivated again and the logical value for the decelerationfuel-cutoff set back, whereas the idle speed control is reactivatedagain at third instant t₃ and its logical value is set.

It is also possible, of course, that a lower gradient of the roadstretch was a contributing factor in the reduction of differencev_act−v_setpoint as well. At fourth instant t₄ following third instantt₃, difference v_act−v_setpoint then drops below third predefined speeddifference DVLLVU, so that the idle speed control will be deactivatedagain at fourth instant t₄ as well and its logical value set back tozero. Between fourth instant t₄ and a subsequent fifth instant t₅,difference v_act−v_setpoint reaches a minimum that is greater than zeroand smaller than third predefined speed difference DVLLVU. Betweenfourth instant t₄ and fifth instant t₅, driving speed control 20 istherefore able again to be realized by a torque request mrfgr_w≧0.Between fourth instant t₄ and fifth instant t₅, idle speed control,deceleration fuel-cutoff and service brake 1 are deactivated. Differencev_act−v_setpoint increases again up to fifth instant t₅, so that torquerequest mrfgr_w of driving speed control 20 is reduced once more. Atfifth instant t₅, difference v_act−v_setpoint exceeds second predefinedspeed difference DVLLVO, so that torque request mrfgr_w has returned tozero at fifth instant t₅, and idle speed control 5 is reactivated bysetting the logical value.

Starting with fifth instant t₅, difference v_act−v_setpoint rises oncemore and at a sixth instant t₆, which follows fifth instant t₅, exceedsfourth predefined speed difference DVSAVO again. As a result, idle speedcontrol 5 is reactivated at sixth instant t₆ by having its logical valuereset to zero, and the deceleration fuel-cutoff is reactivated bysetting of its logical value. Service brake 1 remains deactivated.Starting with sixth instant t₆, difference v_act−v_setpoint continues toincrease and exceeds first predefined speed difference KLDVBROB atseventh instant t₇, which follows sixth instant t₆. At seventh instantt₇, service brake 1 will therefore be activated, the logical value ofthe brake request being set at seventh instant t₇. The decelerationfuel-cutoff remains activated as before, so that service brake 1 isaided by the engine brake realized by the deceleration fuel-cutoff.Shortly after seventh instant t₇, difference v_act−v_setpoint reaches amaximum above first predefined speed difference KLDVBROB and then dropsin a relatively steep manner due to the braking action and possibly as aresult of a downhill slope whose gradient is decreasing again. At aneighth instant t₈ which follows seventh instant t₇, differencev_act−v_setpoint then drops below the predefined switch-off instantDVLLVUBR, so that service brake 1 is deactivated at eighth instant t₈,the logical value of the brake request is set back to zero, thedeceleration fuel-cutoff is deactivated as well and the logical valuereset to zero, the idle speed control deactivated, the logical valueremaining set back. Starting with eighth instant t₈, driving speedcontrol 20 may then be implemented again with the aid of torque requestmrfgr_w, which begins to rise again beginning with eighth instant t₈.

The profile of difference v_act−v_setpoint in FIG. 3 a has been selectedas an example and may result from a road section that has downhillgradients of different magnitudes; between instant t=0 and fourthinstant t₄, a low gradient is present, and between fifth instant t₅ andeighth instant t₈ a more pronounced gradient occurs, which also resultsin a greater difference v_act−v_setpoint.

Furthermore, in the example in FIGS. 3 a-3 e it can be seen that thedeceleration fuel-cutoff is activated as well when service brake 1 isactivated, but not idle speed control 5.

According to the described exemplary embodiment, the driving speedcontrol has a stepped profile. As difference v_act−v_setpoint of thedriving speed increases, the initial response is a reduction of thetorque request of driving speed control 20, followed in a second step byactivation of idle speed control 5, and thus a reduction of the torquerequest of activated ancillary components, followed in a third step bydeceleration fuel-cutoff and thus an interruption of the fuel injectionin this example and, finally, in a fourth step, an activation of theservice brake. It need not necessarily be the case that all mentionedsteps are initiated as a function of the maximally achieved differencev_act−v_setpoint; this will depend on the predefined speed differencesthat are exceeded by the difference v_act−v_setpoint.

The exemplary embodiment shown in FIGS. 3 a-3 e does not include thestep according to FIG. 2 in which additional ancillary components areswitched in when the sixth predefined speed difference is exceeded.Important for the present invention is the activation of the servicebrake when difference v_act−v_setpoint of the driving speed exceeds thefirst predefined speed difference. The additional steps of activation ofthe deceleration fuel-cutoff, activation of the idle speed controland/or activation of one or a plurality of further ancillary componentsmay be provided optionally and in addition, in any desired combination.If the steps of deceleration fuel-cutoff and idle speed control are bothprovided, it is possible - as described in FIGS. 3 a-3 e—to deactivatethe idle speed control when deceleration fuel-cutoff is activated.

The step according to FIG. 3 b in which the torque request is modifiedconstitutes the usual driving speed control, which according to thepresent invention is aided by the service brake and possibly the enginebrake in those instances only where the difference v_act−v_setpoint ofthe driving speed exceeds the corresponding predefined speed differencesand a pure adaptation of the torque request is no longer sufficient tocontrol the driving speed.

If service brake 1 is activated, difference v_act−v_setpoint in thespecific embodiment according to FIGS. 3 a-3 e is reduced in that thenormal closed-loop control of vehicle control 20 is resumed by varyingthe torque request according to FIG. 3 b only when the service brake hasbeen deactivated again at eighth instant t₈ on account of differencev_act−v_setpoint dropping below predefined switch-off point DVLLVUBR.Only following eighth instant t₈ will an engine torque then be requestedagain by vehicle control 20. Due to the fact that according to FIG. 3 eand FIG. 3 d deceleration fuel-cutoff is activated as well betweenseventh instant t₇ and eighth instant t8 when service brake 1 isactivated, and, according to FIG. 3 c, idle speed control 5 isdeactivated when deceleration fuel-cutoff is activated, both thehysteresis of the idle speed control and the hysteresis of decelerationfuel-cutoff are deactivated in the exemplary embodiment of FIGS. 3 a-3 egiven an activated service brake 1. The exemplary embodiment of FIGS. 3a-3 e implements the flow chart according to FIG. 2, with the soleexception that—as described—in the exemplary embodiment according toFIGS. 3 a-3 e the step of switching in one or a plurality of additionalancillary components when difference v_act−v_setpoint of the vehiclespeed exceeds the sixth predefined speed difference is not realized.

The predefined speed differences may be suitably selected or applied insuch a way, for instance, that the idle speed control sets in only whenthe torque request of driving speed control 20 has already been reduceddown to zero, and the deceleration fuel-cutoff only sets in when alltorque requests of activated ancillary components have already beenreduced to zero with the aid of idle speed control 5. The firstpredefined speed difference may be specified such that, for instance,the activation of service brake 1 occurs only when the engine brakingaction realized by the deceleration fuel-cutoff and possibly furtheractivation of one or a plurality of ancillary components has alreadyreached a maximum value.

1. A method for controlling a speed of a vehicle, comprising: when anactual speed of the vehicle exceeds a predefined setpoint speed by morethan a first predefined speed difference, activating a service brake ofthe vehicle, wherein the first predefined speed difference has a valuegreater than zero, and when the actual speed exceeds the setpoint speedby a second predefined speed difference, which is smaller than the firstpredefined speed difference, activating an idle speed control andreducing a torque request of activated ancillary components.
 2. Themethod according to claim 1, further comprising deactivating the idlespeed control when a difference between the actual speed and thesetpoint speed drops below a third predefined speed difference, which issmaller than the second predefined speed difference.
 3. The methodaccording to claim 1, further comprising deactivating the idle speedcontrol for as long as the service brake is activated.
 4. The methodaccording to claim 1, further comprising, when the actual speed exceedsthe setpoint speed by a fourth predefined speed difference, which issmaller than the first predefined speed difference, activating adeceleration fuel-cutoff.
 5. The method according to claim 4, furthercomprising deactivating the deceleration fuel-cutoff when a differencebetween the actual speed and the setpoint speed drops below a fifthpredefined speed difference, which is smaller than the fourth predefinedspeed difference.
 6. The method according to claim 4, wherein the fourthpredefined speed difference is greater than the second predefined speeddifference, and further comprising deactivating the idle speed controlwhen the deceleration fuel-cutoff is activated.
 7. The method accordingto claim 4, wherein the deceleration fuel-cutoff remains activated foras long as the service brake is activated.
 8. A method for controlling aspeed of a vehicle, comprising: when an actual speed of the vehicleexceeds a predefined setpoint speed by more than a first predefinedspeed difference, activating a service brake of the vehicle, wherein thefirst predefined speed difference has a value greater than zero, andwhen the actual speed exceeds the setpoint speed by a sixth predefinedspeed difference, which is smaller than the first predefined speeddifference, activating an ancillary component.